Electrode catheters have been in common use in medical practice for many years. They are used to stimulate and map electrical activity in the heart and to ablate sites of aberrant electrical activity.
In use, the electrode catheter is inserted into a major vein or artery, e.g., femoral artery, and then guided into the chamber of the heart which is of concern. Within the heart, the ability to control the exact position and orientation of the catheter tip is critical and largely determines how useful the catheter is.
Steerable tip electrode catheters are now well known. Such a catheter generally has a control handle at its proximal end for controlling deflection of the tip in one or more directions. For example, U.S. Pat. No. 4,960,134 to applicant discloses a particularly useful steerable tip catheter. This catheter comprises a puller wire which extends on-axis through an elongated reinforced catheter body and then off-axis in a deflectable tip portion. In this arrangement, longitudinal movement of the puller wire relative to the catheter body results in deflection of the catheter tip portion. The catheter body tends not to deflect for two reasons. First, it is reinforced and therefore resists compression. Second, the puller wire extends coaxially within the catheter body. The compressive forces on the catheter body are generally uniformly distributed across the catheter body and deflection is thereby minimized. This allows precise rotational control of the catheter body and tip.
In certain applications, it is desirable to have the ability to inject and/or withdraw fluid through the catheter. This is accomplished by means of an open lumen catheter. For example, it is known that in cardiac ablation procedures using radiofrequency (RF) energy, there is a tendency for the ablation electrode to overheat. If overheating occurs, a coagulum forms on the surface of the electrode and the catheter must be withdrawn, cleaned and reinserted for proper use.
It is known that the ablation electrode can be cooled by the passage of a cooling fluid, e.g., saline solution, through a lumen in the electrode. In a small diameter ablation catheter, e.g., 8 French or less, the size of a lumen sufficient to pass a cooling fluid through the catheter to cool the ablation electrode is such that it does not permit the presence of an on-axis puller wire. That is, the puller wire must extend through the catheter off-axis. In such a catheter, longitudinal movement of the puller wire relative to the catheter body results in not only deflection of the tip, but of the catheter body itself. This makes rotation of the catheter, particularly if the catheter is curved around a vascular bend, exceedingly difficult to control. Thus, conventional designs for small diameter catheters with deflectible tips cannot provide for an open lumen without loss of tip control.